Question

I’m trying to XOR binary values but for some unknown reason I’m losing the first 0 in the conversion. Any idea of what I’m doing wrong?

m1 = int('01010100011001010111001101110100',2)
c1 = int('00111001000001000001000000000001',2)
c2 = int('00111101000100110000110000010001',2)

kk = bin(m1 ^ c1)[2:]
xx = int(kk,2)

m2 = bin(xx ^ c2)[2:]
print m2

For some reason this returns 1010000011100100110111101100100 instead of 01010000011100100110111101100100, so I am losing the leading 0.

Answer 1

Python doesn’t know how many bits you want in the answer. Tell it:

m2 = format(bin(xx ^ c2)[2:],'0>32')

The format string indicates a right-aligned, 32-character field padded with zeroes.

See the Format Specification Mini-Language.

In fact, you can just do the following with the b format specifier:

m1 = int('01010100011001010111001101110100',2)
c1 = int('00111001000001000001000000000001',2)
c2 = int('00111101000100110000110000010001',2)

print format(m1 ^ c1 ^ c2,'0>32b')

or alternatively:

print '{:0>32b}'.format(m1 ^ c1 ^ c2)